The present invention relates to technology for continuously performing a variable control of rotation phase of a camshaft relative to a crankshaft for an internal combustion engine, such as an apparatus for continuously performing a variable control of opening and closing timing of intake and exhaust valves by changing rotation phase of a cam shaft relative to a crankshaft.
A conventional valve timing apparatus is known as a vane type valve timing controlling apparatus disclosed in Japanese Unexamined Patent Publication No. 10-141022.
This apparatus forms concave portions in the inner surface of a cylindrical housing fixed to a cam sprocket in which vanes of an impeller are accommodated in the concave portions wherein the camshaft rotates relative to the cam sprocket within the range where the vanes of the impeller can move in the concave portions and by relatively supplying and discharging oil into a pair of oil pressure chambers, the vanes are held in the mid position of the concave portions and thus successive changing of rotation phase can be carried out.
When oil pressure of the pair of the oil pressure chambers is adjusted to the level by which a target value of rotation phase can be obtained, a control valve closes an oil pressure passage to stop supplying and discharging oil.
PID (proportional-integral derivative) control is generally adopted as control method of the camshaft rotation phase wherein a control amount is calculated with a deviation (error amount) between an actual angle and a target angle of the camshaft as only one variable.
However, in order to carry out the PID control with a good response characteristic it is preferable that a feedback gain is set variable since viscosity of oil changes with oil temperature and oil pressure, but matching the setting as above is not easy.
In the case of oil pressure control there is wide operation dead band for a switching valve (spool valve) to switch oil supply and oil discharge and therefore dither control is executed with dither components in addition to PID to go beyond the dead band wherein judgement of addition of dither components is required to do with accuracy, bringing a complicated control and more capacity of ROM and RAM. In order to decrease variations of dead band width for each part for securing control accuracy, improvement in machining for parts is required, causing increase of machining costs.
In view of the foregoing the present invention has an object of carrying out a valve timing control with higher robust by restraining influences due to disturbances in a valve timing control apparatus for an internal combustion engine.
To achieve the above object, the present invention comprises elements as follows.
A feedback correction amount for feedback controlling a rotation phase of a camshaft relative to a crankshaft to a target value is calculated by sliding mode.
The rotation phase is feedback controlled to a target value using the calculated feedback correction amount.
With this, the opening and closing timings of intake and exhaust valves are continuously and variably controlled.
According to the constitution, based on the feedback control calculated by the sliding mode control, the control with higher robust can be carried out with less influence due to disturbances compared with a feedback control by an ordinary PID control.
The constitution may be such that a rotation phase of the camshaft is controlled by means of a switching valve which is disposed in the oil passage for selectively controlling supply and discharge of oil to an oil pressure actuator to be oil-pressure controlled.
By selectively switching supply and discharge of oil to the oil pressure actuator to be oil-pressure controlled, a driving direction of the oil pressure actuator is switched and also by adjustment of oil amount to an oil chamber, the rotation phase of the camshaft is continuously and variably controlled.
In such a constitution, by application of the sliding control to the oil pressure control mechanism, a control with high robust can be executed avoiding influences due to disturbances such as variations of a dead band of the switching valve, oil temperature, oil pressure and the like. Accordingly a machining accuracy of components can be lowered and machining costs can be reduced.
The sliding mode control may be adapted to switch a feedback gain so that a state of the control system is led to the switching line corresponding to the state of the control system.
According to this constitution, since a switch of the feedback gain is made to guide the state of the control system to the pre-set switching line, the control system can converge to a target value with a good response characteristic sliding along the switching line.
The sliding mode control may be constituted to calculate a feedback correction amount using a non-linear term calculated based on a switching function and a linear term.
With this, a sliding mode can be generated along the switching line by the non-linear term, while adjusting, by the linear term, a velocity of the state of the control system approaching the switching line.
The switching function may be calculated as a function of a deviation between a target position and an actual position of a control object.
With this, by using the deviation between the target position and the actual position for the switching function, the control amount (non-linear term) corresponding to the deviation can be given, resulting in that a complicated dither control to go beyond the dead band of the switching valve (spool valve) is not necessary and capacities of ROM and RAM can be saved. Although conventionally a matching is required for both a PID control and a dither control, it is required only for a sliding mode control and development costs and time can be reduced.
The above switching function S may be calculated by the following equation.
S=xcex3xc3x97PERR+d(PERR)/dt
xcex3: inclination
PER: error amount of the control object
d (PERR)/dt: differential value of the deviation between the target position and the actual position
Thus since the switching function S includes the deviation (PERR) between the target value and the actual value of the control object and also the differential value d (PERR)/dt of the deviation, it is possible to make the sliding mode along the switching line more smooth.
Or, the switching function S may be calculated in the following equation.
S=xcex3xc3x97PERR+d(VTCNOW)/dt
xcex3: inclination
PERR: deviation between the target position and the actual position of the control object
d (VTCNOW)/dt: actual velocity of the control object
Thus, even when an actual velocity is used as a differential value of the control object position, instead of the differential value of the deviation d (PERR)/dt, it is also possible to make a sliding mode control along a switching line smooth.
An inclination of the switching function is set to vary corresponding to states of the control system.
According to this constitution, by variably setting the inclination of the switching function S, a cosine component toward the origin (target value), which is formed cooperatively by the switching line and a direction to the switching line from opposite sides of the switching line (S=0), can get large according to the state of the control system, to thereby promote convergence to a target value (a target angle of VTC) and improve the response characteristic.
Other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments when read in conjunction with the accompanying drawings.